This invention relates to a cover for a manhole structure and more particularly to such a cover which requires a minimum of metal to provide the required strength with the overall weight of the composite cover being of a predetermined minimum weight.
As is well known in the art to which our invention relates, manhole covers are exposed to heavy traffic and must be of a certain minimum weight or else must be secured to the manhole frames by suitable securing means in order to prevent them from becoming dislodged by vehicles passing thereover. Heretofore, this required minimum weight of the manhole cover has been attained by the use of conventional cast iron supporting structures. Now that it is possible to reduce the weight of manhole covers by the use of high strength materials and improved designs, the weight of such covers are often considerably below the minimum weight required to hold the same in place without additional securing means.